U.S. patent application number 11/246151 was filed with the patent office on 2006-08-24 for image forming apparatus.
This patent application is currently assigned to Fuji Xerox Co., Ltd.. Invention is credited to Yoshiki Matsuzaki, Yoshio Yamaguchi.
Application Number | 20060187292 11/246151 |
Document ID | / |
Family ID | 36912244 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060187292 |
Kind Code |
A1 |
Matsuzaki; Yoshiki ; et
al. |
August 24, 2006 |
Image forming apparatus
Abstract
An image forming apparatus has an image carrier, an exposure
array, a reading sensor and a detecting unit. The image carrier
carries a toner image. The exposure array forms a latent image. The
reading sensor reads a pattern. The reading sensor is provided
integrally with the exposure array. The detecting unit detects
fluctuation based on the pattern read by the reading sensor.
Inventors: |
Matsuzaki; Yoshiki;
(Ebina-shi, JP) ; Yamaguchi; Yoshio; (Ebina-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Fuji Xerox Co., Ltd.
Tokyo
JP
|
Family ID: |
36912244 |
Appl. No.: |
11/246151 |
Filed: |
October 11, 2005 |
Current U.S.
Class: |
347/111 |
Current CPC
Class: |
G03G 15/5033 20130101;
G03G 2215/0119 20130101; G03G 2215/0161 20130101; G03G 2215/00075
20130101; G03G 2215/00063 20130101 |
Class at
Publication: |
347/111 |
International
Class: |
B41J 2/385 20060101
B41J002/385 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2005 |
JP |
2005-042892 |
Claims
1. An image forming apparatus comprising: an image carrier that
carries a toner image; an exposure array that forms a latent image,
the exposure array being disposed along an axial direction of the
image carrier; a first reading sensor that reads a first pattern,
the first pattern being provided at uniform intervals along a
peripheral direction and formed substantially parallel to the axial
direction at a region, the region being excepted from a region
where the latent image is formed, the first reading sensor being
provided integrally with the exposure array; and a speed
fluctuation detecting unit that detects surface speed fluctuations
of the image carrier based on the first pattern read by the first
reading sensor.
2. The image forming apparatus according to claim 1, further
comprising: a first correcting unit that corrects writing timing of
the exposure array based on the fluctuations detected by the speed
fluctuation detecting unit.
3. The image forming apparatus according to claim 2, wherein a
correction signal whose phase is different than a phase of the
fluctuations is generated and correction is carried out based on
the correction signal.
4. The image forming apparatus according to claim 1, further
comprising: a second correcting unit that corrects an angular
velocity at which the image carrier is driven based on the
fluctuations.
5. The image forming apparatus according to claim 4, wherein a
correction signal whose phase is different than a phase of the
fluctuations is generated and correction is carried out based on
the the correction signal.
6. An image forming apparatus comprising: an image carrier that
carries a toner image; an exposure array that forms a latent image,
the exposure array being disposed along an axial direction of the
image carrier; a second reading sensor that reads a second pattern,
the second pattern being provided along a peripheral direction and
formed so as to intersect the axial direction at a region, the
region being excepted from a region where the latent image is
formed, the second reading sensor being provided integrally with
the exposure array; and a position fluctuation detecting unit that
detects axial direction positional fluctuations of the image
carrier with respect to the exposure array based on the second
pattern.
7. The image forming apparatus according to claim 6, further
comprising: a third correcting unit that corrects exposure
positions of the exposure array in the axial direction of the image
carrier based on the fluctuations detected by the position
fluctuation detecting unit.
8. The image forming apparatus according to claim 7, wherein a
correction signal whose phase is different than a phase of the
fluctuations is generated and correction is carried out based on
the correction signal.
9. An image forming apparatus comprising: an image carrier that
carries a toner image; an exposure array that forms a latent image,
the exposure array being disposed along an axial direction of the
image carrier and; an image sensor reads a third pattern, the third
pattern being provided at uniform intervals along a peripheral
direction at a region, the region being excepted from a region
where the latent image is formed, the image sensor being provided
integrally with the exposure array; and a detecting unit that
detects axial direction positional fluctuations and surface speed
fluctuations of the image carrier with respect to the exposure
array based on the third pattern read by the image sensor.
10. An image forming apparatus comprising: an image carrier that
carries a toner image; an exposure array that forms a latent image,
the exposure array being disposed along an axial direction of the
image carrier; a reading sensor that reads a pattern, the reading
sensor being provided integrally with the exposure array, the
pattern being provided along a peripheral direction at a region,
and the region being excepted from a region where the latent image
is formed; and a fluctuation detecting unit that detects
fluctuations of the image carrier based on the pattern.
11. The image forming apparatus according to claim 10, further
comprising; a correcting unit that corrects exposure based on the
fluctuations detected by the fluctuation detecting unit.
12. The image forming apparatus according to claim 11, wherein the
correcting unit generates a correction signal whose phase is
different than a phase of the fluctuations, and the correcting unit
carries out correction based on the correction signal.
13. The image forming apparatus according to claim 10, wherein the
pattern has a pattern which is provided at uniform intervals along
the peripheral direction and is formed substantially parallel to
the axial direction, and the fluctuation detecting unit has a speed
fluctuation detecting unit which detects surface speed fluctuations
of the image carrier on the basis of the pattern information read
by the reading sensor.
14. The image forming apparatus according to claim 13, further
comprising: a correcting unit that corrects writing timing of the
exposure array on the basis of the speed fluctuations detected by
the speed fluctuation detecting unit.
15. The image forming apparatus according to claim 13, further
comprising: a correcting unit that corrects an angular velocity at
which the image carrier is driven based on the speed
fluctuations.
16. The image forming apparatus according to claim 10, wherein the
pattern has a pattern which is provided along the peripheral
direction and is formed so as to intersect the axial direction, and
the fluctuation detecting unit has a position fluctuation detecting
unit which, on the basis of the pattern information read at the
reading sensor, detects axial direction positional fluctuations of
the image carrier with respect to the exposure array.
17. The image forming apparatus according to claim 16, further
comprising: a correcting unit that corrects exposure positions of
the exposure array in the axial direction of the image carrier, on
the basis of the axial direction positional fluctuations detected
at the position fluctuation detecting unit.
18. The image forming apparatus according to claim 10, wherein the
pattern has a first pattern which is provided at uniform intervals
along the peripheral direction and is formed substantially parallel
to the axial direction, and a second pattern which is provided
along the peripheral direction and is formed so as to intersect the
axial direction, the reading sensor has a first reading sensor
reading the first pattern, and a second reading sensor reading the
second pattern, and the fluctuation detecting unit has a speed
fluctuation detecting unit detecting surface speed fluctuations of
the image carrier on the basis of pattern information read at the
first reading sensor, and a position fluctuation detecting unit
detecting axial direction positional fluctuations of the image
carrier with respect to the exposure array on the basis of pattern
information read at the second reading sensor.
19. The image forming apparatus according to claim 18, further
comprising: a correcting unit that corrects exposure positions of
the exposure array in the axial direction of the image carrier, on
the basis of the speed fluctuations detected at the speed
fluctuation detecting unit and the axial direction positional
fluctuations detected at the position fluctuation detecting
unit.
20. The image forming apparatus according to claim 10, wherein the
reading sensor has an image sensor reading the pattern, and the
fluctuation detecting unit has a detecting unit which, on the basis
of pattern information read at the image sensor, detects axial
direction positional fluctuations and surface speed fluctuations of
the image carrier with respect to the exposure array.
21. The image forming apparatus according to claim 10, wherein the
image carrier is substantially cylindrical.
22. An image forming apparatus comprising: an image carrier that
carries a toner image; an exposure array that forms a latent image;
a reading sensor that reads a pattern, the reading sensor being
provided integrally with the exposure array; and a detecting unit
that detects fluctuation based on the pattern read by the reading
sensor.
23. The image forming apparatus according to claim 22, wherein the
pattern is provided at uniform intervals along a peripheral
direction and formed substantially parallel to an axial direction
at a region, the region is excepted from a region where the latent
image is formed.
24. The image forming apparatus according to claim 22, wherein the
fluctuation has surface speed fluctuation of the image carrier or
axial direction positional fluctuation of the image carrier.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 USC 119 from
Japanese Patent Application No. 2005-42892, the disclosure of which
is incorporated by reference herein.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to an image forming apparatus
equipped with plural image output devices.
[0004] 2. Related Art
[0005] The following method has conventionally been proposed in a
registration control system in an image forming apparatus which is
equipped with plural image output devices. Patterns for determining
a position of an image are determined in advance by respective ROSs
(Raster Output Scanners) and then sampled by a CCD. A difference
between the positional relationship of the patterns which has no
color offset and the sampled data is detected. By using the the
detected difference, the writing timings of the ROSs, or the
optical positions, are corrected. This method thereby provides good
image quality in which there is little registration offset.
SUMMARY
[0006] The present invention provides an image forming apparatus
which can accurately detect fluctuations in the speed of a drum
surface at an exposure position.
[0007] The image forming apparatus has an image carrier, an
exposure array, a reading sensor and a detecting unit. The image
carrier carries a toner image. The exposure array forms a latent
image. The reading sensor reads a pattern. The reading sensor is
provided integrally with the exposure array. The detecting unit
detects fluctuation based on the pattern read by the reading
sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of the present invention will be described in
detail based on the following figures, wherein:
[0009] FIG. 1 is a schematic diagram showing an image forming
apparatus relating to embodiments of the present invention;
[0010] FIG. 2 is a perspective view showing an exposure array and a
circumferential direction reading sensor of an image forming
apparatus relating to a first embodiment of the present
invention;
[0011] FIG. 3 is a diagram in which the exposure array, the
circumferential direction reading sensor, and a surface of a
photosensitive drum of the image forming apparatus relating to the
first embodiment of the present invention are expanded along a
circumferential direction;
[0012] FIG. 4 is a schematic diagram showing the structure of the
circumferential direction reading sensor of the image forming
apparatus relating to the first embodiment of the present
invention;
[0013] FIG. 5 is a block diagram showing the relationships between
a control section, the exposure array and the circumferential
direction reading sensor of the image forming apparatus relating to
the first embodiment of the present invention;
[0014] FIG. 6 is a flowchart showing operation of the image forming
apparatus relating to the first embodiment of the present
invention;
[0015] FIG. 7A is a diagram for explaining fluctuations in angular
velocity of the photosensitive drum, in which the surface of the
photosensitive drum of the image forming apparatus relating to the
first embodiment of the present invention is expanded along the
circumferential direction, and FIG. 7B is a diagram for explanation
of correcting the fluctuations in the angular velocity of the
photosensitive drum;
[0016] FIG. 8 is a perspective view showing a modified example of
the exposure array and the circumferential direction reading sensor
of the image forming apparatus relating to the first embodiment of
the present invention;
[0017] FIG. 9 is a perspective view showing an exposure array and a
circumferential direction reading sensor of an image forming
apparatus relating to a second embodiment of the present
invention;
[0018] FIG. 10 is a diagram in which the exposure array, the
circumferential direction reading sensor, and a surface of a
photosensitive drum of the image forming apparatus relating to the
second embodiment of the present invention are expanded along a
circumferential direction;
[0019] FIG. 11 is a diagram for explaining axial direction offset
of the photosensitive drum, where the surface of the photosensitive
drum of the image forming apparatus relating to the second
embodiment of the present invention is expanded along the
circumferential direction;
[0020] FIGS. 12A, 12B and 12C are diagrams for explaining
correcting of axial direction offset of the photosensitive
drum;
[0021] FIG. 13 is a perspective view showing a first modified
example of correcting axial direction offset of the photosensitive
drum;
[0022] FIGS. 14A and 14B are perspective views showing a second
modified example of correcting axial direction offset of the
photosensitive drum;
[0023] FIG. 15 is perspective view showing a third modified example
of correcting axial direction offset of the photosensitive
drum;
[0024] FIG. 16 is a perspective view showing a modified example of
the circumferential direction reading sensor;
[0025] FIG. 17A is a diagram in which the surface of the
photosensitive drum shown in FIG. 16 is expanded along the
circumferential direction, and FIG. 17B is a diagram for explaining
axial direction offset of the photosensitive drum;
[0026] FIG. 18 is a perspective view showing a method of correcting
circumferential direction offset of the photosensitive drum in real
time; and
[0027] FIG. 19 is a diagram in which the surface of the
photosensitive drum of FIG. 18 is expanded along the
circumferential direction.
DETAILED DESCRIPTION
[0028] A color image forming apparatus according to a first
embodiment of the present invention is shown in FIG. 1.
[0029] FIG. 1 is a schematic structural diagram showing a
tandem-type digital color printer 10 serving as the color image
forming apparatus.
[0030] Image forming units 13Y, 13M, 13C, 13K of the respective
colors of yellow (Y), magenta (M), cyan (C), and black (K), which
serve as image forming units, are lined-up at uniform intervals
along the horizontal direction at the interior of the digital color
printer 10. When there is no need to differentiate between Y, M, C,
K, the letters Y, M, C, K will be omitted.
[0031] An intermediate transfer belt 25 is disposed, beneath the
four image forming units 13Y, 13M, 13C, 13K. The toner images of
the respective colors, which are formed successively by these image
forming units, are transferred onto the intermediate transfer belt
25 in a state of being superposed one on another.
[0032] Then, the toner images of the respective colors, which are
transferred in a superposed manner on the intermediate transfer
belt 25, are transferred all at once onto a recording sheet 34
which serves as a recording medium and which is fed-out from a
sheet feed tray 39 or the like. Thereafter, the superposed toner
images are fixed onto the recording sheet 34 by a fixing device 37,
and the recording sheet 34 is discharged to the exterior.
[0033] The image forming units 13Y, 13M, 13C, 13K are basically
structured by photosensitive drums 15Y, 15M, 15C, 15K which serve
as image carriers and which rotate at predetermined rotational
speeds along the directions of the arrows; scorotrons 12Y, 12M,
12C, 12K for primary charging which uniformly charge the surfaces
of the photosensitive drums 15Y, 15M, 15C, 15K; exposure arrays
14Y, 14M, 14C, 14K which expose images corresponding to the
respective colors on the surfaces of the photosensitive drums 15Y,
15M, 15C, 15K so as to form electrostatic latent images; developing
devices 17 which develop the electrostatic latent images formed on
the photosensitive drums 15Y, 15M, 15C, 15K; and cleaning devices
18.
[0034] Next, main portions of the image forming apparatus relating
to the first embodiment of the present invention will be
described.
[0035] As shown in FIGS. 2 and 3, lines, which are parallel to the
axial direction of the photosensitive drum 15, are formed at one
end side of the photosensitive drum 15 at predetermined intervals
along the circumferential direction of the photosensitive drum 15.
(Hereinafter, these lines are called a "circumferential direction
formed pattern 40").
[0036] A circumferential direction reading sensor 42 is provided
integrally with the one end portion of the exposure array 14
positioned above the photosensitive drum 15. The circumferential
direction reading sensor 42 is disposed at a position facing the
circumferential direction formed pattern 40 which is formed on the
one end portion of the photosensitive drum 15.
[0037] As shown in FIG. 4, the circumferential direction reading
sensor 42 has a lens 44 which collects light, and a light-receiving
portion 46 which receives reflected light. The circumferential
direction reading sensor 42 collects light, which is emitted by an
LED (not shown) on the surface of the photosensitive drum 15 by the
lens 44 (at a so-called detecting position, a central line P (see
FIG. 3) of the circumferential direction formed pattern 40), and
the light which reaches the surface of the photosensitive drum 15
and is reflected thereat is incident on the light-receiving portion
46.
[0038] The photosensitive drum 15 is formed of aluminum. Therefore,
the reflectance of light toward the light-receiving portion 46 is
high at the portions where the circumferential direction formed
pattern 40 is not formed, and the reflectance of light reflected to
the light-receiving portion 46 is low at the circumferential
direction formed pattern 40. The presence/absence of the
circumferential direction formed pattern 40 can be confirmed by the
difference of the reflectance of the light toward the
light-receiving portion 46.
[0039] Here, as shown in FIG. 5, the circumferential direction
reading sensor 42 is connected to a control section 48. Information
read by the difference in the reflectance of the light reflected
toward the light-reflecting portion 46 (i.e., data expressing the
presence/absence of the circumferential direction formed pattern
40) is inputted to the control section 48 (step 100 of FIG. 6).
[0040] As shown in FIG. 3 (FIG. 3 is a diagram in which the surface
of the photosensitive drum 15 is expanded along the circumferential
direction), the circumferential direction formed pattern 40 is
formed at predetermined intervals along the circumferential
direction of the photosensitive drum 15. Therefore, as the
photosensitive drum 15 rotates, the presence/absence of the
circumferential direction formed pattern 40 is detected
alternately. Because the photosensitive drum 15 is rotating at a
given rotational speed, the circumferential direction formed
pattern 40 is detected at the same interval. The surface speed of
the photosensitive drum 15 is detected by the interval of the
detected circumferential direction formed pattern 40 (step 102 of
FIG. 6).
[0041] By providing the circumferential direction reading sensor 42
integrally with the exposure array 14 as shown in FIG. 2, the
exposure array 14 and the circumferential direction reading sensor
42 can be positioned as a fixed positional relationship.
[0042] Therefore, the positional relationship between the exposure
array 14 and the circumferential direction reading sensor 42 does
not change due to, for example, fluctuations in the position of the
exposure array 14 due to errors in the mounting of the exposure
array 14 or fluctuations in the temperature within the digital
color printer 10 (see FIG. 1), or the like.
[0043] Accordingly, the surface speed of the photosensitive drum 15
can be detected accurately along the circumferential direction of
the photosensitive drum 15. The accuracy of detection is improved,
and accordingly, the accuracy of correcting periodic fluctuations
(so-called AC fluctuations) in the subscanning direction is
improved.
[0044] Further, with regard to the distance between the exposure
array 14 and the photosensitive drum 15, highly-accurate mounting
is required from the standpoint of limits on the focal depth
(.+-.0.1 mm). Therefore, by providing the exposure array 14 and the
circumferential direction reading sensor 42 integrally, the
mounting accuracy of the circumferential direction reading sensor
42 with respect to the photosensitive drum 15 also improves. Thus,
the adjusting of the focal depth of the circumferential direction
reading sensor, which has an enlarging/reducing optical system (the
lens 44 (see FIG. 4)), can be carried out with high accuracy, and
the accuracy of detection can be improved.
[0045] FIG. 7A is a diagram in which the surface of the
photosensitive drum 15 is expanded along the circumferential
direction. A circumferential direction formed pattern 50, which is
read at the circumferential direction reading sensor 42, is
supposed to be the same interval as a circumferential direction
formed pattern 52 (the dotted lines) which is shown at the
originally designed position. However, when the surface speed of
the photosensitive drum 15 fluctuates due to an eccentricity or the
like, an offset Pe (see FIG. 7A) arises with respect to the
circumferential direction formed pattern 52 at the designed
position.
[0046] As shown in FIG. 7B, the control section 48 computes the
fluctuations in the surface speed of the photosensitive drum 15, or
the positional fluctuations in the circumferential direction caused
thereby, as phase data 54 along the circumferential direction of
the photosensitive drum 15 (the direction of arrow A) (step 104 of
FIG. 6). Further, the control section 48 computes reverse phase
data 56 which offsets this phase data 54 (step 106 of FIG. 6).
[0047] As shown in FIG. 5, the control section 48 is connected to
the exposure array 14. As a first correcting unit, the control
section 48 changes the writing timing of the exposure array 14
(step 108 of FIG. 6), on the basis of the reverse phase data 56
which is computed by the control section 48 and which is with
respect to fluctuations in the angular velocity computed from the
surface speed fluctuations of the photosensitive drum 15. In this
way, the fluctuations in the angular velocity of the photosensitive
drum 15 are offset, and the fluctuations can be made to be
small.
[0048] Although the circumferential direction reading sensor 42 is
provided integrally with the one end portion of the exposure array
14 here, it suffices to position the exposure array 14 and the
circumferential direction reading sensor 42 as a fixed positional
relationship. Therefore, the present invention is not limited to
the above-described structure. For example, as shown in FIG. 8, the
exposure array 14 and the circumferential direction reading sensor
42 may be fixed to a flat-plate-shaped supporting member 58.
[0049] In the present embodiment, the writing timing of the
exposure array 14 is changed on the basis of the reverse phase data
56 with respect to the fluctuations in the angular velocity of the
photosensitive drum 15. However, because it suffices to make the
fluctuations in the angular velocity of the photosensitive drum 15
small, the present invention is not limited to the same. For
example, as a second correcting unit, the rotational speed of a
motor 60 which is connected to the photosensitive drum 15 can be
varied on the basis of the reverse phase data 56 with respect to
the fluctuations in the angular velocity of the photosensitive drum
15, and the fluctuations in the angular velocity of the
photosensitive drum 15 can be made to be small.
[0050] Next, main portions of an image forming apparatus relating
to a second embodiment of the present invention will be described.
Some parts are substantially the same as those of the first
embodiment of the present invention will be omitted.
[0051] As shown in FIGS. 9 and 10 (FIG. 10 is a diagram in which
the surface of the photosensitive drum 15 is expanded along the
circumferential direction), in addition to the circumferential
direction formed pattern 40, an axial direction formed pattern 62,
which is inclined with respect to the axial direction of the
photosensitive drum 15, is formed at one end side of the
photosensitive drum 15 at the inner side of the circumferential
direction formed pattern 40. The axial direction formed pattern 62
is disposed at predetermined intervals along the circumferential
direction of the photosensitive drum 15.
[0052] On the other hand, the circumferential direction reading
sensor 42 and an axial direction reading sensor 64 are provided
integrally at one end portion of the exposure array 14. The
circumferential direction reading sensor 42 and the axial direction
reading sensor 64 are disposed so as to face the circumferential
direction formed pattern 40 and the axial direction formed pattern
62, respectively, and can detect fluctuations in the angular
velocity of the photosensitive drum (rotational direction offset)
as well as axial direction offset of the photosensitive drum 15.
Here, the structure of the axial direction reading sensor 64 is the
same as that of the circumferential direction reading sensor 42, so
the description thereof will be omitted.
[0053] FIG. 11 is a diagram in which the surface of the
photosensitive drum 15 is expanded along the circumferential
direction. An axial direction formed pattern 66, which is read at
the axial direction reading sensor 64, is originally supposed to be
the same interval as the axial direction formed pattern 62 (the
dotted lines) which is shown at the designed position. However,
when the axial direction position of the photosensitive drum 15
differs in the circumferential direction of the photosensitive drum
15 due to mounting errors or the like, an offset Xe (see FIG. 11)
arises with respect to the axial direction formed pattern 62 which
is at the designed position.
[0054] Since this offset (Xe) includes the offset (Pe) which is due
to the fluctuations in the angular velocity of the photosensitive
drum 15, an offset amount (Le) of the axial direction formed
pattern 66 is a value obtained by subtracting the offset (refer to
Pe (FIG. 7A)) in the circumferential direction of the
photosensitive drum 15 due to the angular velocity fluctuations,
from the offset (Xe) with respect to the axial direction formed
pattern 62 at the designed position. The axial direction offset of
the photosensitive drum 15 can be computed on the basis of this
offset amount (Le).
[0055] Here, by providing the circumferential direction reading
sensor 42 and the axial direction reading sensor 64 integrally with
the exposure array 14 as shown in FIGS. 9 and 10, the exposure
array 14, and the circumferential direction reading sensor 42 and
the axial direction reading sensor 64 can be positioned as a fixed
positional relationship.
[0056] Therefore, the positional relationship between the exposure
array 14, and the circumferential direction reading sensor 42 and
the axial direction reading sensor 64 does not change due to
fluctuations in the position of the exposure array 14 or the like.
Accordingly, the angular velocity and the axial direction position
of the photosensitive drum 15 can be calculated accurately along
the circumferential direction of the photosensitive drum 15. The
accuracy of detection is improved, and accordingly, the accuracy of
correcting periodic fluctuations (so-called AC fluctuations) in the
main scanning direction and the subscanning direction is
improved.
[0057] Namely, the control section 48 computes the angular velocity
and the axial direction offset of the photosensitive drum 15
respectively as phase data 54 along the circumferential direction
of the photosensitive drum 15, and computes reverse phase data 56
which offsets this phase data 54.
[0058] Then, on the basis of the reverse phase data 56 which is
computed by the control section 48 and which is with respect to
fluctuations in the angular velocity of the photosensitive drum 15,
the control section 48 changes the writing timing of the exposure
array 14. Further, on the basis of the reverse phase data which is
computed by the control section 48 and which is with respect to the
axial direction offset of the photosensitive drum 15, as shown in
FIGS. 12A through 12C, the control section 48 changes the range of
the LEDs 68 which are used, and changes the write positions (shown
by the black circles) of the exposure array 14 as a third
correcting unit.
[0059] In this way, the fluctuations in the angular velocity of the
photosensitive drum 15 are offset, and these fluctuations are made
to be small. Further, the axial direction offset of the
photosensitive drum 15 is offset, and this offset can be made to be
small.
[0060] Note that the embodiments are strictly examples, and it goes
without saying that appropriate modifications can be made within a
scope which does not deviate from the gist of the present
invention.
[0061] In the present embodiment, the write positions of the
exposure array 14 are changed on the basis of the reverse phase
data with respect to the axial direction offset of the
photosensitive drum 15. However, it suffices to be able to make the
axial direction offset of the photosensitive drum 15 small, so the
present invention is not limited to the embodiments as mentioned
above.
[0062] For example, the exposure array 14 itself may be made to be
movable along the axial direction of the photosensitive drum 15.
Concretely, as shown in FIG. 13, the following structure may be
employed: a piezoelectric element 70 connected to the control
section 48 is disposed at the other end portion of the exposure
array 14. An end portion of a piezoelectric holding member 71,
which holds the piezoelectric element 70, is fixed to a fixing
member 73. Thus, when voltage is applied to the piezoelectric
element 70, the piezoelectric element 70 flexurally deforms toward
the exposure array 14. The exposure array 14 is moved along the
axial direction of the photosensitive drum 15 in accordance with
the amount of flexural deformation of the piezoelectric element
70.
[0063] Further, as shown in FIGS. 14A and 14B, the following
structure may be employed: a ball screw 74, which is connected to a
motor 72 which is connected to the control section 48, is
screwed-into an exposure array 14 side nut 75 at the other end
portion of the exposure array 14. Due to the motor 72 rotating, the
ball screw 74 is rotated, and the exposure array 14 is moved along
the axial direction of the photosensitive drum 15 via the nut
75.
[0064] Still further, as shown in FIG. 15, the following structure
may be employed: a rack 76 juts out at the other end portion of the
exposure array 14. A pinion 80, which is connected to a motor 78
which is connected to the control section 48, meshes with the rack
76. Due to the motor 78 rotating, the exposure array 14 is moved
along the axial direction of the photosensitive drum 15 via the
pinion 80 and the rack 76.
[0065] In the present embodiment, as shown in FIGS. 2 and 3, light
is collected at the central line P of the circumferential direction
formed pattern 40 by using the circumferential direction reading
sensor 42. However, as shown in FIGS. 16 and 17A (FIG. 17A is a
diagram in which the surface of the photosensitive drum 15 is
expanded along the circumferential direction), the circumferential
direction formed pattern 40 and an axial direction formed pattern
84, which is formed along the circumferential direction at a
predetermined position in the axial direction of the photosensitive
drum 15 at the outer side of the circumferential direction formed
pattern 40, may be read as image data by using a CCD sensor 82.
[0066] In this case, the following structure can be employed in
order to broaden the reading region: even though the axial
direction formed pattern 84 is a straight line running along the
circumferential direction of the photosensitive drum 15, by
determining the amount of offset between the axial direction formed
pattern 84 and a reading reference line Q, an offset amount .delta.
(see FIG. 17B) in the axial direction of the photosensitive drum 15
can be detected.
[0067] Moreover, in the present embodiment, for example, the
angular velocity of the photosensitive drum 15 is computed as the
phase data 54 along the circumferential direction of the
photosensitive drum 15, the reverse phase data 56 which offsets the
phase data 54 is computed, and the fluctuations in the angular
velocity of the photosensitive drum 15 are made to be small.
However, because it suffices to be able to make the fluctuations in
the angular velocity of the photosensitive drum 15 small, the
present invention is not limited to this method.
[0068] FIGS. 18 and 19 show an example of correcting, in real time,
fluctuations in the surface speed which arise due to eccentricity
of the photosensitive drum 15. Fluctuations in the surface speed
due to eccentricity are the same fluctuations at the same positions
of the photosensitive drum 15. Therefore, at the circumferential
direction reading sensor 42 and the exposure array 14, the
positions with respect to the circumferential direction of the
photosensitive drum 15 are made to be offset, and the fluctuations
in speed immediately before exposure are detected by the
circumferential direction reading sensor 42. On the basis of these
results of detection, the exposure timing for exposing the
photosensitive drum 15 is corrected.
[0069] Namely, a first aspect of the present invention is an image
forming apparatus comprising: an image carrier carrying a toner
image; an exposure array disposed along an axial direction of the
image carrier and forming a latent image; a first reading sensor
provided integrally with the exposure array, and reading a first
pattern which is provided at uniform intervals along a peripheral
direction and which is formed parallel to the axial direction at an
outer side of a region of the image carrier where the latent image
is formed; and a speed fluctuation detecting unit detecting surface
speed fluctuations of the image carrier, on the basis of pattern
information read at the first reading sensor.
[0070] In the first aspect, the exposure array, which is disposed
along the axial direction of the image carrier and forms a latent
image, and the first reading sensor, which reads the first pattern
which is provided at uniform intervals along the peripheral
direction of the image carrier, are provided integrally.
Fluctuations in the surface speed of the image carrier can be
detected by the speed fluctuation detecting unit from the pattern
information read by the first reading sensor.
[0071] By providing the exposure array and the first reading sensor
integrally, the exposure array and the first reading sensor can be
positioned as a fixed positional relationship. Therefore, the
positional relationship between the exposure array and the first
reading sensor does not change due to, for example, positional
fluctuations of the exposure array caused due to errors in the
mounting of the exposure array or temperature fluctuations within
the image forming apparatus, or the like.
[0072] Accordingly, the surface speed of the image carrier at the
exposure position along the peripheral direction of the image
carrier can be detected accurately. The accuracy of detection is
improved, and accordingly, the accuracy of correcting periodic
fluctuations (so-called AC fluctuations) in the peripheral
direction of the image carrier is improved.
[0073] Further, with regard to the distance between the exposure
array and the image carrier, highly-accurate mounting is required
from the standpoint of limits on the focal depth (.+-.0.1 mm).
Therefore, by providing the first reading sensor integrally with
the exposure array, the mounting accuracy of the first reading
sensor with respect to the image carrier also improves. Thus, the
adjusting of the focal depth of the first reading sensor, which has
an enlarging/reducing optical system, can be carried out with high
accuracy, and the accuracy of detection can be improved.
[0074] The image forming apparatus of the first aspect of the
present invention may be provided with a first correcting unit
correcting a writing timing of the exposure array, on the basis of
the speed fluctuations detected at the speed fluctuation detecting
unit.
[0075] In accordance with this structure, the writing timing of the
exposure array is corrected by the first correcting unit on the
basis of the results of detection of the speed fluctuation
detecting unit. In this way, it is possible to correct periodic
fluctuations (AC fluctuations), in the image carrier peripheral
direction, of the image which are caused by surface speed
fluctuations which are detected by the speed fluctuation detecting
unit.
[0076] The image forming apparatus of the first aspect of the
present invention may be provided with a second correcting unit
which, on the basis of the speed fluctuations detected at the speed
fluctuation detecting unit, corrects an angular velocity at which
the image carrier is driven.
[0077] In accordance with this structure, on the basis of the
results of detection of the speed fluctuation detecting unit, the
second correcting unit computes the angular velocity of the image
carrier, and corrects the angular velocity of the image carrier. In
this way, it is possible to correct periodic fluctuations (AC
fluctuations), in the image carrier peripheral direction, of the
image which are caused by surface speed fluctuations which are
detected by the speed fluctuation detecting unit.
[0078] At the above-described correcting unit, on the basis of the
speed fluctuations detected at the speed fluctuation detecting
unit, a correction signal, whose phase is different than the speed
fluctuations, may be generated, and correction may be carried out
on the basis of the correction signal.
[0079] In accordance with this structure, a correction signal,
whose phase is different than that of the surface speed
fluctuations of the image carrier, is generated on the basis of
results of detection of the speed fluctuation detecting unit. By
correcting the speed fluctuations on the basis of this correction
signal, the surface speed fluctuations of image carrier are made to
be small.
[0080] A second aspect of the present invention is an image forming
apparatus comprising: an image carrier carrying a toner image; an
exposure array disposed along an axial direction of the image
carrier and forming a latent image; a second reading sensor
provided integrally with the exposure array, and reading a second
pattern which is provided along a peripheral direction and which is
formed so as to intersect the axial direction at an outer side of a
region of the image carrier where the latent image is formed; and a
position fluctuation detecting unit which, on the basis of pattern
information read at the second reading sensor, detects axial
direction positional fluctuations of the image carrier with respect
to the exposure array.
[0081] In the above-described second aspect, the second pattern is
formed at an incline with respect to the axial direction of the
image carrier, and is provided at uniform intervals along the
peripheral direction. The second reading sensor, which reads the
second pattern, is provided. From the pattern information read by
the second reading sensor, the position fluctuation detecting unit
can detect the axial direction positional offset of the image
carrier with respect to the exposure array.
[0082] In the same way as in the detection of periodic fluctuations
in the peripheral direction of the image carrier, by providing the
exposure array and the second reading sensor integrally, the
positional relationship between the exposure array and the second
reading sensor does not change due to positional fluctuations of
the exposure array or the like.
[0083] Accordingly, the axial direction fluctuations of the image
carrier with respect to the exposure array can be detected
accurately. The accuracy of detection is improved, and accordingly,
the accuracy of correcting periodic fluctuations (so-called AC
fluctuations) in the axial direction of the image carrier is
improved.
[0084] The image forming apparatus of the second aspect may have a
third correcting unit correcting exposure positions of the exposure
array in the axial direction of the image carrier, on the basis of
the axial direction positional fluctuations detected at the
position fluctuation detecting unit.
[0085] In accordance with this structure, on the basis of the
results of detection of the speed fluctuation detecting unit, the
third correcting unit corrects the exposure positions of the
exposure array in the axial direction of the image carrier. The
axial direction positional offset of the image carrier with respect
to the exposure position can thereby be corrected. In this case,
the exposure positions may be changed by changing the
light-emitting positions of the exposure array, or the position of
the exposure array itself may be shifted along the axial direction
of the image carrier.
[0086] In the above-described correcting unit, on the basis of the
positional fluctuations detected at the position fluctuation
detecting unit, a correction signal, whose phase is different than
the positional fluctuations, may be generated, and correction may
be carried out on the basis of the correction signal.
[0087] In accordance with this structure, a correction signal,
whose phase is different than that of the axial direction
positional fluctuations of the image carrier, is generated on the
basis of results of detection of the position fluctuation detecting
unit. By correcting the positional fluctuations on the basis of
this correction signal, the axial direction positional fluctuations
of image carrier are made to be small.
[0088] A third aspect of the present invention is an image forming
apparatus comprising: an image carrier carrying a toner image; an
exposure array disposed along an axial direction of the image
carrier and forming a latent image; an image sensor provided
integrally with the exposure array, and reading a third pattern
which is provided at uniform intervals along a peripheral direction
at an outer side of a region of the image carrier where the latent
image is formed; and a detecting unit which, on the basis of
pattern information read at the image sensor, detects axial
direction positional fluctuations and surface speed fluctuations of
the image carrier with respect to the exposure array.
[0089] In the third aspect, the third pattern is provided at
uniform intervals along the peripheral direction of the image
carrier. The image sensor which reads the third pattern is
provided. From the pattern information read by the image sensor,
the detecting unit can detect the surface speed fluctuations and
the axial direction positional fluctuations of the image carrier
with respect to the exposure array.
[0090] By providing the exposure array and the image sensor
integrally, the positional relationship between the exposure array
and the image sensor does not change due to positional fluctuations
of the exposure array or the like.
[0091] Accordingly, the surface speed and the axial direction
fluctuations of the image carrier with respect to the exposure
array can be detected accurately. The accuracy of detection is
improved, and accordingly, the accuracy of correcting periodic
fluctuations (so-called AC fluctuations) in the axial direction and
the surface speed of the image carrier is improved.
[0092] Because the present invention is structured as described
above, in the first aspect of the present invention, by providing
the exposure array and the first reading sensor integrally, the
exposure array and the first reading sensor can be positioned as a
fixed positional relationship. Therefore, the surface speed of the
image carrier at the exposure position along the peripheral
direction of the image carrier can be detected accurately. The
detection accuracy is improved, and accordingly, the accuracy of
correcting the periodic fluctuations (so-called AC fluctuations) in
the peripheral direction of the image carrier is improved.
[0093] In the second aspect of the present invention, by providing
the exposure array and the reading sensor integrally, the
positional relationship between the exposure array and the second
reading sensor does not change due to positional fluctuations of
the exposure array or the like. Therefore, axial direction
fluctuations of the image carrier with respect to the exposure
array can be detected accurately. The detection accuracy is
improved, and accordingly, the accuracy of correcting the periodic
fluctuations (so-called AC fluctuations) in the axial direction of
the image carrier is improved.
[0094] In the third aspect of the present invention, by providing
the exposure array and the reading sensor integrally, the
positional relationship between the exposure array and the image
sensor does not change due to positional fluctuations of the
exposure array or the like. Therefore, the surface speed and axial
direction fluctuations of the image carrier with respect to the
exposure array can be detected accurately. The detection accuracy
is improved, and accordingly, the accuracy of correcting the
periodic fluctuations (so-called AC fluctuations) in the axial
direction and the surface speed of the image carrier is
improved.
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